Acrylic companionway sliding hatch?

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I'm curious about acrylic sliding hatches, as I'd like to build one for my boat. I'm in the process of putting a new deck on her and have a curved aluminum hatch that drips condensation, tries to throw you overboard if you stand on it, has a lip edge that catches lines... and doesn't have a dog house. So in the next couple days I'll be tooling up to change that.

I'd like to know the span width of some of the late model production boats companionways, and the width of where the acrylic rides on the track, and if they leak everywhere in rain and spray, as most I've looked at in pictures don't appear to have much in the way of a drain channel.

So far my noodling is to make a mold (screw some coosa board strips down from the backside to a plywood bench top make the part as one piece, with a cross bar or two temporarily tabbed to it so the frame stays parallel then work the core parallel to the part, and have a flat lid for it to form the dog house.

It looks like most of the production boats are using 1/2 inch smoked acrylic, with an inch and a quarter to inch and three quarter overlap on the runners... So spitballing numbers, a 27 inch wide opening would be a 30 inch wide piece of acrylic.

Anyone have any insight as far as how tight things ought to fit, or any known gotchas with this type design?

A lot of pictures I've seen don't appear to have anything that holds the hatch slide downward and just lay into place, or have a tight fitting groove and god only knows where the drainage lines go.

Other than the vertical clearance to the boards that form the top, anything to it? The new Beneteau Oceanis style designs are simple enough looking that I'm at a bit of a loss if there isn't a c-channel hidden inside a drain channel to hold things down, unless the front end under the dog house just fits tight enough not to lift at the back, but given the boards over the top sit an inch or so higher than the acrylic I've got a hard time believing that there isn't something holding things down tight, less a wave coming aboard lifting the slider and giving you an inch wide gap to wet down the interior...

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The detail you drew will not work. Water will flow outboard to the edge of the hatch, surface tension will keep it adhered to the underside of the Lexan and it will drip into the companionway at rates that will boggle the mind.

There are several solutions, all of them involving considerable work. Gun posted one alternative, although I don't really see how that works when the yacht is heeled with the starboard rail down in the sketch he provided. Water will rest in the slot and drip on through.

The best designs I've seen are those in which the outboard edges of the slider have a lip that protrudes below the stationary surface on which the hatch slides. This forces water to shed except when there's positive pressure from boarding waves and there's no real solution for that with a sliding hatch.

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There are several solutions, all of them involving considerable work. Gun posted one alternative, although I don't really see how that works when the yacht is heeled with the starboard rail down in the sketch he provided. Water will rest in the slot and drip on through.

Edited:
I can see what you mean about water resting in the slot, its never been a problem so far - the water tends to run aft alone the slot and then into the drainage channel.
I'm probably not sailing it hard enough.

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Thanks for that guys, sounds like a uhmw slider screwed to the underside, with a drip edge might be salvation. I've always wondered about the teflon tape self adhesive stuff that some shops sell for sliding hatches, so it may be that it's a double number.

It does actually remind me of a boat I looked at a few years back, a condor 40 trimaran. It had a hatch on rails much wider than the companionway, with a heavy weight plastic with a straight slot cut in it... but the rails and hatch were 6+ inches offset outboard of the opening into the boat. It was a chin scratcher at that moment, but in light of new information it makes sense.

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The detail you drew will not work. Water will flow outboard to the edge of the hatch, surface tension will keep it adhered to the underside of the Lexan and it will drip into the companionway at rates that will boggle the mind.

There are several solutions, all of them involving considerable work. Gun posted one alternative, although I don't really see how that works when the yacht is heeled with the starboard rail down in the sketch he provided. Water will rest in the slot and drip on through.

The best designs I've seen are those in which the outboard edges of the slider have a lip that protrudes below the stationary surface on which the hatch slides. This forces water to shed except when there's positive pressure from boarding waves and there's no real solution for that with a sliding hatch.

I have a Beneteau with this type of arrangement and I replaced my Lexan hatch a few years ago with a new one. It seems to be OK, but I've never been too concerned about water down below, to be honest. I wonder if cutting a couple slots along the length of the hatch cover parallel to the tracks would eliminate the potential of water adhesion as you mention? Provided there is enough overhang on the hatch, that is.

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The new slider will be flat, so it'll be easy to replace the acrylic if need be at a later date. That'll take a little bit of finagling to get the height of the slides higher than the camber of the deck.

Part of the desire is to have a hatch turtle that you can stand on, that is also flat. I'm thinking with the style pictured above, that the cover boards could extend forward and become the hatch turtle. I've got some 1/2 inch divinycell kicking around and a bit of leftover core mat, so the hatch turtle would be walkable.

Right now the curve of the hatch has more camber than the the rest of the deck. It looks good, but trying to stand on it is like trying to balance on the top of a water pipe. Even with non-skid it tries to spit you overboard.